(Adds new review, detail)
By Sarah N. Lynch, Mark Hosenball and Andy Sullivan
WASHINGTON, Dec 9 (Reuters) - The U.S. Justice Department's internal watchdog said it found numerous errors but no evidence of political bias by the FBI when it opened an investigation into contacts between Donald Trump's presidential campaign and Russia in 2016.
The report by Inspector General Michael Horowitz was likely to give ammunition to both Trump's supporters and his Democratic critics in the ongoing debate about the legitimacy of an investigation that shadowed the first two years of his presidency.
Horowitz found that the FBI had a legal "authorized purpose" to ask for court approval to begin surveillance of Carter Page, a Trump campaign adviser.
But Horowitz also found a total of 17 "basic and fundamental" errors and omissions in the original application and all subsequent renewals to the Foreign Intelligence Surveillance Court (FISA). Those errors made the case appear stronger than it was, Horowitz said.
In particular, the report singled out an FBI lawyer who altered an email contained in a renewal of the application which claimed that Page was "not a source" to another U.S. government agency.
In truth, Page served as a "operational contact" to another unnamed agency, which was not named in the report.
The FBI investigation, launched in the summer of 2016 ahead of the November election pitting Trump against Democratic candidate Hillary Clinton, was taken over in May 2017 by former FBI chief Robert Mueller after Trump fired James Comey as the agency's director.
Mueller's 22-month special counsel investigation detailed a Russian campaign of hacking and propaganda to sow discord in the United States, harm Clinton and boost Trump. Mueller documented numerous contacts between Trump campaign figures and Moscow but found insufficient evidence of a criminal conspiracy.
Trump called the investigation, known within the FBI as Crossfire Hurricane, a witch hunt and assailed FBI leaders and career staffers who worked on it.
Democrats have accused Trump of seeking to discredit a legitimate investigation that detailed extensive interactions between his campaign and Russia and long cast a cloud over his presidency.
"The FBI had an authorized purpose when it opened Crossfire Hurricane to obtain information about, or protect against, a national security or federal crime, even though the investigation also had the potential to impact constitutionally protected activity," Horowitz's report said.
FBI Director Christopher Wray agreed with all of the inspector general's findings. Attorney General William Barr said the report "reflects a clear abuse of the FISA process."
"The Inspector General's report now makes clear that the FBI launched an intrusive investigation of a U.S. presidential campaign on the thinnest of suspicions," Barr said in a statement.
Horowitz said his office on Monday launched a new review to further scrutinize the FBI's compliance with its own fact-checking policies used to get applications to surveil U.S. persons in counterterrorism investigations, as well as counterintelligence probes.
The FBI opened Crossfire Hurricane on July 31, 2016, after getting a tip from a foreign ally that Trump adviser George Papadopoulos suggested he had gotten offers of help from the Kremlin.
When it asked for court permission to open a wiretap on Page, Horowitz found that the FBI relied heavily on research assembled by former British intelligence officer Christopher Steele.
While the FBI had reason to believe that Steele was reliable as it had worked with him before, the agency did not reassess his information when it sought to renew its warrants, the report said, and did not press him about who was funding his work.
Steele assembled his dossier for an opposition-research firm that was funded by the Democratic Party. Trump's allies say the FBI should have disclosed that fact in its warrant application.
Horowitz's report will not be the final word on the subject. Barr in May appointed John Durham, a federal prosecutor in Connecticut, to examine whether the Russia investigation was properly predicated. Durham's work has become a criminal investigation.
(Reporting by Sarah N. Lynch; Additional reporting by Mark Hosenball, Brad Heath and Andy Sullivan; Writing by Andy Sullivan; Editing by Will Dunham and Jonathan Oatis)
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